With the unprecedented wealth of high-resolution protein structures churned out by x-ray crystallographers in the last two decades, it might be easy for a structural biologist to develop a sense of complacency. Not so Dorothee Kern, who sees a real opportunity to augment these otherwise static structural images with new studies designed to reveal what she calls the "dynamic personality" of enzymes, signaling proteins, and the substrates that they affect. Only through such dynamic studies, Kern argues, will researchers develop a realistic picture of how proteins function.
Her primary tool of choice is nuclear magnetic resonance (NMR) spectroscopy, which is capable of observing and recording the motion of the atoms inside functioning proteins. NMR relies on magnetic fields and radio waves to probe the structure, dynamics, and function of molecules.
Colleagues who have followed Kern's work closely describe her as a "pioneer," one who approaches the classical subject of enzymology in a new way. For example, Kern has used NMR spectroscopy to study a signaling molecule called NtrC, whose function is triggered by addition of a phosphate molecule. Her studies have revealed some interesting truths about the mechanism of activation of this signaling protein. It does not merely add a phosphate to create the active structure, but instead already constantly flickers between the inactive and active structure. It is the rarely populated active conformation that gets phosphorylated, resulting in a shift of the conformational equilibrium toward the active state. These studies demonstrate that NMR as a technology is capable of observing more than proteins in motion—it is indispensable for teasing out those particular motions that are directly relevant to protein function.
She has pioneered studies of the dynamics of enzymes during catalysis, moving beyond the traditional concept of enzymes as molecules that simply foster the progress of chemical reactions. Again using NMR, she has measured the high-speed motions of enzymes as they attach to substrate molecules, catalyze their chemical reactions, and release final products. Her new dynamic NMR analytical techniques have enabled her to catch enzymes in the act of changing conformation during catalysis. Such analysis has yielded new insight into how enzymes' conformational rearrangements influence the speed of the catalytic process.
Kern's future plans include dissecting structural features of proteins that determine their motion. She will also explore whether it is possible to determine in greater detail high-energy conformational substrates that enzymes sample during catalysis.
Kern hopes that understanding protein dynamics will have an impact on rational drug design. Her work includes studies of proteins that play key roles in HIV virulence, cancer, and Alzheimer's disease.
